Machinarium

Machinarium is award-winning independent adventure game developed by the makers of Samorost and Botanicula. A little robot who’s been thrown out to the scrap yard behind the city must return and confront the Black Cap Brotherhood and save his robot-girl friend.

I've been playing for 16 hours on and off, saving quite happily. It is now only giving me "Start New Game" as an option and all my previous play is lost. How can I get back into the game? I haven't finished!